The present invention relates to a variable venturi-type carburetor.
The inventor has proposed a variable venturi-type carburetor having a raised wall which projects from the inner wall of the intake passage, which inner wall faces the tip face of the suction piston serving to change the cross-sectional area of the venturi portion of the carburetor in response to a change in the amount of air fed into the cylinder of the engine. In this carburetor, the raised wall has a substantially straight extending tip edge, and the upstream end portion of the tip face of the suction piston is shaped in a V-shaped cross-section which expands toward the venturi portion so that an approximately triangular-shaped air inflow opening is formed between the tip edge of the raised wall and the upstream end portion of the tip face of the suction piston when the amount of air fed into the cylinder of the engine is small. In this carburetor, when the amount of air fed into the cylinder of the engine is small, since the opening area of the air inflow opening is smoothly increased in accordance with the increase in the lift of the suction piston, the amount of air fed into the cylinder of the engine is not abruptly changed and, therefore, it is possible to prevent the output power of the engine from abruptly changing. However, in this carburetor, since the raised wall projects into the intake passage to a great extent, the flow area of the intake passage is small even if the suction piston maximally opens the intake passage and, as a result, a problem occurs in that the volumetric efficiency will be reduced when the amount of air fed into the cylinder of the engine is large.